Friend, much of Science involves mass murder of complex life including mammals, for the express purpose of teasing apart how their individual bits work. If you live near an R1 university, there's very likely a facility nearby dedicated to the raising of lab animals. An ex worked at one that raised rodents and chickens for Michigan State University.

A scientist once confided in me that he became a scientist because as a child he really liked lizards, but as a scientist, he spends much of his time murdering lizards. :-/

Everyone involved has to confront this reality on their own, come to terms with it, and figure out the line where they're willing to meet it. All the researchers I've known have cared deeply about the welfare of the animals, despite sometimes doing terrible things to them for science. They worked to limit their suffering and dispatch them as humanely as possible. Many rationalize it by comparing to the food system, which raises and slaughters orders of magnitude more souls, and keeps people living, but does not discover or record as much new knowledge as science.

Your misguided empathy is dangerous to humanity. So much of the vast genetic magic is hidden purely because we tie our hands behind our backs. Each day these secrets are withheld is another day tens of thousands of humans die from potentially trivial diseases and conditions. Further millions suffer in their broken minds for decades with no solace, all because we chose to extend our empathy in instantly gratified, short sighted ways. I say we go further, withdraw our empathy towards the worst among us; those that have hurt their fellow man, and make their bodies available for study and experimentation, both dead and alive.